PICAXE simulating even if not connected to power in model?


New Member

Apologies if this is a silly question.

I have an 08M circuit modelled in PICAXE VSM and it seems to simulate fairly well. However, I have put a switch on the 5V supply line to the 08M to test things in the model but the PICAXE simulates even when not connected to power.

Is there a way to fix this?



Senior Member
On a real chip, parasitic power from a connection to pins other than the power pins can cause the picaxe to run. I have no idea whether the simulation in VSM is complete enough to replicate this "feature".


New Member
Thanks for the info.

I've just tried a new model with the 08M not connected to anything. It still tries to simulate, although an error comes up that the RXD pin is floating. Once that is connected to ground the chip simulates code fine, even though it's not connected to anything else.

This probably doesn't come up very often, but I'm essentially using the power connection as another input so in this case it's annoying.


Senior Member
Have you tried...

I don't have a copy of VSM, but I have an (old) copy of Proteus which is what PicAxe VSM is based on.

Loading a project in this with a PIC16F1829 (which is the processor the 20M2 is based upon) doesn't show the power pins at all. The power connections are implied. If I right click on the processor and select "Edit Properties", there is an option for "Hidden Pins", clicking on this allows the hidden VDD (+5V) and VSS (Gnd) pins to be connected to a specific net. If you were to name the wire from the switch to something like "Sw5V" and then change the net name for the hidden "VDD" pin so it is connected to your "Sw5V" net it may work as intended. It may not, but worth a try perhaps?


Technical Support
Staff member
In all VSM microcontroller models the power supply is implied, that's just the way it is designed. As stated above in many components the power pins are hidden, so that is why the behavior is like this.